This invention relates to cartridges for providing a liquid to be dispensed and to devices for and methods of dispensing a liquid from such cartridges, such as a liquid containing medicaments and drugs. In a preferred embodiment, such liquids are dispensed to the eye of a user.
A variety of devices for dispensing liquid are known. Exemplary devices for dispensing a liquid to the eye of a user are disclosed in, e.g., U.S. Pat. Nos. 3,087,656; 3,788,528; 4,623,337; 4,811,866; and 4,925,065. Included among these devices are both multi-dose and single-dose devices.
Multi-dose devices pose problems with product sterility, e.g., when the device is used repeatedly to dispense liquid to the eye. Although practically all such devices and their contents are sterile before they are opened for use, not only is the product within the dispenser no longer sterile after opening but there is danger of contamination of the contents by the user, as well as cross-contamination where several people, e.g., family members, use the same dispensing device.
Some commercially available single-dose devices are sold with instructions that the user discard the device after one use. However, many such single dosage units hold over 350 .mu.l of liquid and dispense on an average 50 .mu.l of liquid per drop, leaving more than 300 .mu.l of liquid after a single use or about 250 .mu.l when both eyes are treated. The user is often reluctant to discard a device still more than half full, resulting in reuse of a single-dose device. Reuse not only negates the purpose of single-dose dispensing but also greatly increases the danger of contamination and product deterioration, since single-dose devices, once opened, typically cannot be reclosed for a tight seal.
Maintaining sterility of the product to be dispensed is not only necessary to prevent contamination but is also a desirable feature to reduce or eliminate the need for a preservative.
In addition to the sterility problems inherent in known devices for dispensing liquid to the eye of a user, most such devices are neither easy nor convenient to use. Anyone who has ever had to apply drops of liquid to the eye is aware of the difficulty and inconvenience typically experienced with currently available devices. Frequently, the drop misses the targeted eye and the procedure must be repeated. Furthermore, such devices suffer deficiencies both in volume of liquid delivered as well as reproducibility of the amount of liquid dispensed. Both of these deficiencies translate into dosage problems when the liquid contains a medication.
Volume of liquid dispensed by dispensing devices on the market today, typically droplets of liquid in excess of 35 .mu.l and some as high as 56 .mu.l, results in waste. Since the eye can only hold 25 .mu.l, see, e.g., Keister et al., Journal of Pharmaceutical Sciences, 80 (1991) 50-53, anything in excess of 35 .mu.l will be wasted. Even in cases where cost is not a factor, droplet size can be important, e.g., in cases where the efficiency of a medication is greatly enhanced with a droplet size of about 10 .mu.l (See, e.g., Keister et al., supra).
Since presently known devices for the delivery of liquids to the eye suffer disadvantages which include sterility maintenance, imprecise delivery, and ease of use alternative dispensing devices are being sought.